Traffic zone surveillance computer



Aug. 29, 1967 J. H. AUER, JR

TRAFFIC ZONE SURVEILLANCE `COMPUTER 4 Sheets-Sheet l Filed July l5, 1965 HIS ATTORNEY Aug. 29, 1967 J. H. AUER, JR 3,339,061

TRAFFIC ZONE SURVEILLANCE COMPUTER Filed July l5, 1963 4 Sheets-Sheet 2 AVERAGE SPEED F IG- 3 COMPUTERl II INPUT FROM| g1 III F|G.4 DETECTOR IIr MH I VOLUMEDIFFERENOE INPUT FROM IOO OUTPUT COM PU TER DETECTOR 2 T-r |02 g INPUT FROM |23 T46 NEGATIVE PULSE ,2| GENERATOR 2S I A I INPUT FROM |22 |24 405 'O9 l POSITIVE PULSE L- GENERATOR 27 FIG I FIGO NEGATIVE PULSE POSITIVE PULSE GENERATOR GENERATOR R I4 INPUT FROM l/ OUTPUT INPUT FROM PUTPUT TO Q -i--IAH TO RELAY (-)I RELAY DETIEICTOR CONTACT |7 DETEZCTOR CONTACT I8 @BILT I I (+)i '30 'vf- WO 5' I T Liu-47A( IIVOLME -EI-HJQ/[OTLELMWETO T DIFF RENCE 'f- I l- COMPUTER 46 Jggggjgg TYPICAL ANALOG COMPARATOR INPUTl 4l JHAUER kIR.

HISl ATTORNEY Aug. 29, 1967 `.1.H.AUET\,.1T

` TRAFFIC ZONE SURVEILLANCE COMPUTER 4 sheets-sheet vs' Filed 'July 15, 196s FIG. 9

f AVER/AGING CIRCUIT l FIGB TYPICAL. COUNTER RESET FISIO l ANALOG MEMORY CIRCUIT OUTPUT Dm Y mR .M E WU T I A. m H Mm IU. H

I i I I I COUNTER 24 RESET COUNTER 24 OUTPUT I I l R Dn EN ET TD TE NT .NS UU UE OO OR C C Aug. 29, v1967 J. H; AUER, JR

I TRAFFIC ZONE SURVEILLANCE COMPUTER 4 Sheets-Sheet 4 Filed July 15, 1963 .I I I I IL 9N. mozmm...

no@ J.

I I||||I|| 552 .QQ 1c om.

INVENTOR. BY JHAUER JR.

HIS ATTORNEY kalm@ N OWFZOO Qmmaw United States Patent 3,339,061 TRAFFIC ZONE SURVEILLANCE COMPUTER John H. Auer, Jr., Rochester, N.Y., assignor to The General Signal Corporation, Rochester, N.Y., a corporation of New York Filed .luly 15,1963, Ser. No. 294,936 25 Claims. (Cl. 23S-150.24)

This invention relates to a method and apparatus for maintaining traffic surveillance within a defined Zone, and more particularly to a computation method and apparatus for detecting disruptions and discontinuities in trafiic flow within a traffic lane.

Along vehicular routes handling heavy trafiic it is imperative that smooth traffic flow be maintained at all times, in order to utilize the roadway at its utmost efficiency. This is especially true along routes which provide insufficient opportunity for vehicles to change lanes in order to avoid a slow-moving or stationary obstruction in the travelled lane. Such conditions are most likely to be encountered on bridges or in tunnels, but are also likely to occur along any trafiic route handling high traffic volumes.

Moreover, it is important not only to detect such condition when it occurs, but also to provide information as to approximate location of the obstruction. Heretofore, detection of traffic disruptions and discontinuities, also referred to as tubululent flow, has been achieved by visual observation of the traffic stream. However, this necessitates either placement of personnel in strategic locations along the route, or dispatch of personnel to travel the route in order to locate the obstruction.

When monitoring traffic flow for the purpose of detecting turbulence, it is desirable to ignore gradual, or smooth changes in flow, since such changes are not indicative of turbulence. Under normal, free-flowing trafiic conditions gradual flow changes constantly take place, due to factors such las weather conditions, traffic density, driver idiosyncrasies, etc. However, a discontinuity in the flow of traffic is a condition which should be detected as early as possible, in order that immediate steps may be taken to correct the condition before serious trafiic disruptionV with its attendant consequences results. n

The present invention provides a novel method and apparatus for detecting and approximately locating traffic disruptions and discontinuities along a traffic lane utilizing only two vehicle detectors. A first detector is situated at one end of the portion of the traffic lane to be monitored, and the other is situated at the other end of the portion to be monitored. Computing apparatus is coupled to the detectors and utilizes individualv vehicle detections as a basis for providing information as to location of any obstruction along the portion of the lane under surveillance.

One object of the invention is to` provide a method and apparatus for detecting disruptions and discontinuities in traffic flow along a traffic lane.

Another object is to provide a method and apparatus for approximately determining the location of a traffic obstruction within a traiiic lane.

Another object of the invention is to provide a system which suppliesl early warning of a discontinuity in traffic flow while ignoring gradual; changes in traflic flow.

Another object is to provide computing means for locating an obstruction to trafiic flow along a portion of a traffic lane by comparing the number of vehicles enteringV the portion during a first interval' with the number of vehicles leaving' the portion during a second interval to determine whether of the two counts is greater.

Another object is to provide a method of detecting and locating a traffic obstruction within a trafiic lane by alternately counting the number of vehicles entering a de- 3,339,061 Patented Aug. 29, 1967 ice niarcated portion of the lane during a time interval of duration inversely proportional to vehicular speed and counting the number of vehicles leaving the demarcated portion of the lane during a successive time interval of Iduration inversely proportional to vehicu-lar speed.

Another object is to provide a method and apparatus for detecting presence of a traffic obstruction within a traffic lane by comparing continuously-measured entry and egress trafiic volume at either end of a demarcated portion of the lane.

The invention therefore contemplates a novel system for detecting and locating an obstruction to vehicular travel along a traffic lane comprising means generating odd and even time intervals of duration inversely proportional to average vehicular speed, means totaling the number of vehicles entering a demarcated portion of the lane during each odd interval, and means subtracting the number of vehicles leaving the demarcated portion of the lane during each successive even interval from the total number of vehicles counted during the preceding odd inerval. Means are further provided for detection of traic obstructions by maintaining a continuous comparison between trafiic volumes measured at the entry and egress points of the demarcated portion of the trafiic lane.

The foregoing and other objects and advantages of the invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIG. lis a simplified block diagram of one embodiment l of the computer for detecting and locating a trafiic flow obstruction along a demarcated portion of a traffic lane.

FIG. 2 is a plan view of the demarcated portion of the vehicular route, showing geographical placement of vehicle presence along a single trafiic lane. v

FIG. 3 is a schematic diagram of one type of average speed computer which may be utilized in the system of FIG. l.

FIG. 4 is a schematic diagram of one type of traiiic volume difference computer which maybe used in the system of FIG. l.

FIG. 5 is a schematic diagram of a negative pulse generator which may be utilized in the system of FIG. 1.

FIG. 6 is a schematic diagram of a positive pulsegenerator which may be utilized in the system of IFIG. 1.

FIG. 7 is a schematic diagram of a typical analog comparator used in the system of FIG. l.

FIG. 8 is a schematic diagram of a typical counter used in the system of FIG. 1.

FIG. 9 is 4a schematic diagram of an averaging circuit which may be used in the system of FIG. 1.

FIG. l0 is a schematic diagram of an analog memory which may be used in the system of FIG. 1.

FIG. 11 is a simplified block diagram of a second embodiment of a portion of the computer for detecting and locating a traffic flow obstruction along'a demarcated portion of a traffic lane.

FIG. l2 is a schematic diagram of one form of variable delay unit which may lbe use'd in the system of FIG. l1.

Turning now to FIG. l there is shown a pair of vehicle presence detectors 11 and 12. Both detectors are coupled to a count differential circuit 8 and a volume differential circuit 9'. Detector 11 senses vehicles entering 4a demarcated portion of a traiiic lane while detectorv 12 senses vehicles leaving the demarcated portion of the lane. Physical location of these detectors is illustrated in FIG. 2, wherein detectors 11 and 12 are placed along'a portion 'of a trafiic lane 10. Based on the direction of vehicular travel along thelane, detector I1 is obviously an upstream detector while' detector 12l is aV downstream detector.

For the count differential portion of the system to perform properly, it is necessary that the duration of each time interval used for addition of vehicles entering the demarcated portion of the lane and for subtraction of vehicles leaving the demarcated portion be inversely proportional to detected vehicle speed so that the vehicles subtracted from the counter are, under free-ilowing traffic conditions, the same vehicles that were added to the counter during the preceding interval. Therefore, a method and means for measuring speed and generating a time interval inversely proportional to speed is required. The relationship between speed and time is such that the product of these two must equal the distance between the detectors.

Returning to FIG. 1, the outputs from detectors 11 and 12 are coupled to an average speed computer 13.

The speed computed therein is an average value resulting from measurements made at detectors 11 and 12. This average speed may be obtained by a circuit which,.in eiect, divides traic volume by density. Such lcircuit is explained in greater detail infra.

The output voltage of computer 13 is coupled to a phase inverter 14 4having a voltage gain of one, and thence to a front contact 15 of a relay R1. The output voltage of computer 13 is also directly coupled to back contact 15 of the relay. The heel of contact 15 is coupled to the input of an integrator 20. When relay R1 is deenergized, output voltage of integrator increases in a positive direction at a rate directly proportional to speed as computed by average speed computer 13. On the other hand, in the event relay R1 is energized, the inverse of speed voltage produced by computer 13 is applied to the integrator from phase inverter 14 through front contact 15. This causes the output voltage of integrator 20 to decrease toward zero at -a rate proportional to computed average vehicular speed. Although relay R1 operates satisfactorily in the system, a two-state switch, or gate, having a plural'- ity of input and output terminals may obviously be substituted for the relay, if so desired.

The output from integrator 20 is coupled to an analog comparator circuit 21, providing a first input voltage therefor. A second input voltage to analog comparator 21 is provided from a distance control potentiometer 22 through a back contact 16 of relay R1. The distance control is manually adjusted to a position proportional to the spacing between detectors 11 and 12, and may actually be calibrated in units of length. Hence, beginning with zero output from integrator 20, the integration process continues for a time interval which is terminated when the output voltage of the integrator becomes equal in magnitude or absolute amplitude, to the voltage provided by the distance control. At this time, the polarity of input voltage applied to the comparator reverses. The output voltage amplitude of analog comparator 21 then abruptly changes from a large positive value to a large negative value. This large negative voltage is applied to the input of ahpower amplifier 22, which inverts the polarity of voltage applied thereto. Thus, relay R1 receives a positive voltage from amplifier 22, causing energization.

Energization of relay R1 causes voltage applied to integrator 20 to change polarity while remaining directly proportional in magnitude to average speed. As previously mentioned, this causes the output of the integrator to decrease towards zero at a rate proportional to average vehicle speed as computed by computer 13. Moreover, under these conditions, the negative potential from the distance control is disconnected. This makes it necessary for the output of the integrator to decrease to zero and actually move to a slightly negative potential in order for the output of analog comparator 21 to swing in a positive direction Iso as to deenergize relay R1. This occurs since the change in polarity of voltage applied to the comparator causes an abrupt reversal of polarity at the out'- put of the comparator. Hence, relay R1 remains energized and deenergized for intervals of time inversely proportional to average vehicle speed. The relationship is 'such lthat the product of average vehicle speed and relay time interval is equal to the distance between vehicle detectors.

A pair of counters 24 and 25 is provided. These counters are essentially integrators which serve as staircase type counters in the system. Counter 24 receives inputs from a negative pulse generator 26 through a back contact 17 of relay R1, while counter 25 receives inputs from a positive pulse generator 27 through a back contact 18 of relay R1, when the relay is deenergized. On the other hand, when relay R1 is energized, counter 24 receives inputs from positive pulse generator 27 through front contact 18 of relay R1, while counter 25 receives inputs from negative pulse generator 26 through front contact 17 of the relay. Negative pulse generator 26 produces a negative output voltage pulse each time detector 11 senses a vehicle. Similarly, positive pulse generator 27 produces a positive output voltage pulse each time detector 12 senses a vehicle. Hence, during the time intervals when the relay is deenergized, vehicles sensed by detector 11 are added to counter 24, while vehicles sensed by detector 12 are subtracted from counter 25. During the alternate intervals when relay R1 is energized, vehicles sensed by detector 11 are added to counter 25 and vehicles sensed by detector 12 are subtracted from counter 24. Thus, negative pulses applied to either counter are added by the counter, while positive pulses applied to either counter are subtracted by the counter. Detailed operation of counters 24 and 25 is described infra.

The output voltage from counter 24 is coupled to a front Contact 28 of a relay R2, while output voltage from counter 25 is coupled to a front contact 30 of a relay R3. Both front contacts 28 and 30 are coupled to the input of an analog memory 32. Relay R2 is coupled to a back contact 19 of relay R1, while relay R3 is coupled to front contact 19 of relay R1. The heel of contact 19 is coupled to one side of a capacitor 33, the other side of which is coupled to a source of negative potential. Hence, energization of relay R1 produces momentary energization of relay R3, since a charge stored on capacitor 33 is discharged therethrough. Simila-rly, deenergization of relay R1 produces momentary energization of relay R2, since capacitor 33 acquires a charge therethrough. Steady energization ot either relay R2 or R3 is impossible, since capacitor 33 is always present in the energizing circuit for either relay.

A capacitor 34 is coupled to the heel of a contact 29 of relay R2, and a capacitor 35 is coupled to the heel of a contact 31 of relay R3. Front contact 29 is coupled to a source of positive voltage, while back contact 29 is coupled to counter 24. Similarly, front contact 31 is coupled to to the positive voltage source and back contact 31 is coupled to counter 25. Thus, energization of relay R2 causes capacitor 34 to acquire a charge; deenergization of relay R2 then lcauses the charge stored in capacitor 34 to discharge through counter 24. This capacitor discharge provides a voltage which resets the counter. Similarly, energization of relay R3 causes capacitor 35 to acquire a charge; subsequent deenergization of relay R3 causes discharge of capacitor 35 through counter 25, thereby providing a voltage for resetting the counter.

Upon energization of relay R2, front contact 28 momentarily couples an output signal from counter 24 to analog memory 32. The counter is subsequently lreset by discharge of capacitor 34. Resetting of counter 24 however is slightly delayed, since it occurs upon subsequent deengization of relay R2. Analog memory 32 does not follow the output of counter 24 when it is reset, since resetting does not occur until relay R2 deenergizes, opening the input circuit to the analog memory. 'Ihe -analog memory is now in its HOLD mode, whereby it retains the signal applied thereto from counter 24 prior to resetting of the counter. This signal may be read on a zero-center meter 44, coupled between the output of analog memory 32 and ground. The meter is capable of indicating both positive and negative voltages produced by the analog memory, and may be calibrated in units of vehicles.

The number of vehicles registered on meter 44 represents the difference between the number of vehicles entere ing the demarcated portion of the traflic lane shown in FIG. 2 during a first, or odd interval, and the number of vehicles leaving the demarcated portion during a consecutive second, or even interval. The registered number of vehicles may be a positive or negative number, or zero. A positive number on meter 44 indicates that the number of vehicles entering the demarcated portion of the lane during the first interval is less than the number of vehicles leaving the demarcated portion during the second interval, while a negative number indicates that the number of vehicles leaving the demarcated portion of the lane during the second interval is less than the number of vehicles entering the demarcated portion during the first interval. If the number of vehicles leaving the demarcated portion of the lane during the second interval is equal to the number of vehicles entering the demarcated portion during the first interval, the reading on meter 44 Will be zero. Obviously, if the input connections to meter 44 are reversed, a positive number on the meter then indicates more vehicles have entered the demarcated portion of the lane in the first interval than have left in the second interval, While a negative number indicates more vehicles have left the portion in the first interval than entered in the second interval. The meter input connections may be made therefore simply as a matter of choice.

When relay R1 is actuated to its energized state, relay R3 momentarily energizes and then deenergizes. During the energized interval of relay R3, a voltage of amplitude proportional to the number stored in counter 25 is applied to analog memory 32 through closed front contact 30 of relay R3. The analog memory thus assumes the number stored in counter 25, which can now be read on meter 44. Simultaneously, capacitor 3S acquires a charge through closed front contact 31 of relay R3. Upon deenergization of relay R3, analog memory 32 is again isolated from any input voltage by the opening of front contact 30. This returns the memory to its HOLD mode. Subsequently, back contact 31 of relay R3 closes, resetting counter 24 With the discharge of capacitor 35.

As previously mentioned, when relay R1 is actuated to its deenergized state, vehicles sensed by detector 11 are added to the count in counter 24. Similarly, vehicles sensed by detector 12 are subtracted from the count in counter 25. However, when relay R1 is energized, vehicles sensed by detector 11 are added to the count in counter 25; similarly, vehicles sensed by detector 12 Iare subtracted from the count in counter 24.

The output voltage from analog memory 32 is coupled to a phase inverter 36 having a voltage gain of one. The output voltage from phase inverter 36 is coupled through a diode 37,A poled in the Iforward direction, to a rst input of an analog comparator circuit 39. A second diode 38 is coupled in shunt with the series circuit comprising phase inverter 36 and diode 37, and is also poled in the forward direction. The phase inverter provides positive output voltage for negative input voltages, which are applied to analog comparator 39 through diode 37. These negative analog memory output voltages are blocked by diode 38. On the other hand, when positive voltages are provided by analog memory 32, phase inverter 36 provides negative voltages which are blocked by diode 37. However, the positive voltages are applied to the first input of analog comparator 39 through diode 38. Hence, no matter what the polarity of output voltage from analog memoryv 32, analog comparator 39 receives positive potential at its first input of magnitude substantially equal to that of phase inverter 36` output voltage.

A second input to analog comparator 39 is provided from a count control 40, which comprises a source of two separately adjustable negative voltages. Selection of a voltage for the second input of comparator 39* is made by a switching circuit, such as a relay R4 having a contact 41. Energization of relay R4 causes analog comparator 39 to receive a negative voltage of one amplitude through -front contact '41, while deenergization of relay R4 causes analog comparator 39 to receive a negative voltage of a second amplitude through back contact 41. These amplitudes are selected in accordance with the difference in counts at detectors 11 and 12 which it is desired to detect. In general, it may be desirable to provide a first count difference to actuate an alarm, for example, and a second count difference to turn olf the alarm. Hence, the second count difference is preferably a lower number than the first, in order to positively assure that a detected discontinuity has been cleared before turning off the alarm. The count control may be calibrated in units of vehicles. Comparator 39 provides input voltage to an amplifier 43, the output of which controls energization of relay R4. Thus, when the algebraic sum of voltages applied to the inputs of analog comparator 39 changes sign, output of comparator 39 abruptly changes from a large voltage of one polarity to a large voltage of opposite polarity.

The count differential portion 8 of the computer operates on the basis of information provided by vehicle counts, as already seen. The volume differential portion 9 however, operates on the basis of traffic volume information provided from detectors 11 and 12. Thus, outputs from negative and positive pulse generators 26 and 27 are coupled to the input of a volume difference cornputer 46. This computer compares counts per unit time from detectors 11 and 12 and provides an output voltage directly proportional to the difference between traic volume measured at each end of the demarcated portion of the traffic lane shown in FIG. 2. This computer is described in further detail infra.

Output voltage from volume difference computer 46 is coupled to an averaging circuit 47. This circuit cornprises a long time-constant amplifier which continuously averages the measured volume difference. Output voltage from averaging circuit 47 is presented on a zero-center meter 48 coupled thereto. This meter may be calibrated in units of vehicles per unit time, such as Vehicles per minute. The averaging circuit is explained in greater detail infra.

Output voltage from averaging circuit 47 is applied to a phase inverter 49 having a voltage gain of one, and to a first input of an analog comparator circuit 52 through a forward-connected diode 50. Output voltage from phase inverter 49 is also applied to the first input of analog comparator 52 through a forward-connected diode 51. In fashion identical to that described for phase inverter 36 and diodes 37 and 38, phase inverter 49 operates in combination with diodes 50 and 51 to provide an input voltage to analog comparator 52 which is substantially equal in magnitude to the output voltage of averaging circuit 47, but always of positive polarity, regardless of averaging circuit 47 output voltage polarity.

A second input is supplied to analog comparator S2- from a volume control 53. This control comprises two separate adjustable sources of negative voltage. Each separate source may be calibrated in ter-ms of vehicles per minute. Selection of one or the other voltage for application to comparator 52 is made by a contact 54 of a relay R5. Thus, ener-gization of relay R5 provides a first negative input voltage to analog comparator 52 through front contact 54, while deenergization of relay R5 provides a second negative input voltage to comparator 52 through back contact 54.

In a fashion similar to that already described for analog comparators 21 and 39, output voltage from analog comparator 52 abr-u-ptly changes its polarity `from a limiting level of one polarity to a limiting level of opposite polarity whenever the algebraic sum of input voltages changes polarity. The output voltage from comparator 52 is coupled 4through an amplifier 56 to relay R5.

A front contact 42 of relay R4 and a front contact 55 of relay RS are connected in parallel between the positive voltage source and a circuit coupled to utilization means 57. In utilization means may comprise an alarm circuit, recording means, or any other circuit desired to be operated in response to traiiic disruptions or discontinuities.

Utilization means 57 may be operated in response to only one of front contacts 42 and 55 if desired. In the event front contact 42 is open-circuited, utilization means 57 operates in response to the difference between average traic volumes at detector 11 and detector 12. Similarly, in the event front contact 55 of relay R5 is open-circuited instead of -front contact 42, utilization means 57 operates in response to the difference between vehicle counts at detector 11 for a iirst time interval and vehicle counts at detector 12 for a second time interval. By combining both aforementioned measurements, utilization means 57 provides a more accurate indication of traflic conditions within the demarcated portion of the traiic line.

To summarize operation of the computing system of FIG. 1, detector 11, which senses vehicles entering the demarcated portion of the trafic lane, and `detector 12, which senses vehicles leaving the demarcated portion of the traflic lane, supply inputs to average speed computer 13, enabling the computer to provide an output signal proportional to average vehicle speed. This signal is applied through back contact 15 of relay R1 to integrator 20, which provides a positive output voltage having a positive slope directly proportional to average speed as computed by computer 13 as long as back contact 15 remains closed. Output of integrator is compared with a predetermined negative voltage selected from distance control 22. When the integrator output voltage rises to a magnitude in excess of that provided from distance control 22, the output voltage produced from analog comparator 21 abruptly changes from positive to negative polarity. Amplier 23 then provides a positive output voltage, energizing relay R1. This energization occurs at the end of an interval suiicient for a vehicle to travel from the location of detector 11 to the location of detector 12 at the computed average speed provided by computer 13. This interval may be referred to as the rst interval.

Energization of relay R1 opens back contact 16, removing the negative voltage provided by distance control 22 from analog comparator 21. Simultaneously, average speed voltage from computer 13 is coupled to integrator 20 through phase inverter 14 in series with front contact 1S of relay R1. Thus, during the second interval, or interval in which relay R1 is energized, the inverted speed potential applied to the integrator causes the positive integrator output voltage to decrease toward zero at a rate proportional to computed avera-ge vehicle speed. Since the negative potential from the distance control is disconnected, it is necessary for the output of the integrator to decrease to zero and actually move to a slightly negative potential in order yfor the output of comparator 21 to jump to a positive value and deenergize relay R1. Deenergization of relay R1 demarcates the end of the second time interval and the start of a third time interval, which actually is a repeat of the iirst time interval. Thus, relay R1 remains energized and denergized for equal intervals of time, with the duration of each interval being inversely proportional to vehicle speed in such manner that the product of vehicle speed and time interval is equal to the distance 4between vehicle detectors 11 and 12. Hence, under free-flowing trailic conditions, the vehicles sensed by detector 11 during the rst interval are the same vehicles sensed by detector 12 during the second interval.

During lthe first interval, back contact 17 and 18 of relay R1 are closed. Under these conditions, vehicles sensed -by detector 11 provide negative pulses yfor generator 26 which are coupled to counter 24, subtracting from the count therein. Similarly, vehicles sensed by detector 12 cause generator 27 to produce positive pulses which are added to the count in counter 25. -Each pulse produced by either generator 26 or 27 represents a single vehicle count.

At the end of the iirst interval, relay R1 is energized,

as previously explained. Capacitor 33, which has acquired a charge through relay R2 and back contact 19 of relay R1 during the first interval, now discharges through front contact 19, momentarily energizing relay R3. This in turn causes the count stored in counter 25 to be applied to analog memory 32 through closed front contact 30 of relay R3. The total count may then be read on indicator 36.

Upon deenergization of relay R3, front contact 30 opens, causing analog memory 32 to switch to its HOLD condition. Simultaneously, capacitor 35, having acquired a charge when front contact 31 momentarily closed, now discharges through back contact 31, resetting counter 25 to zero.

While relay R1 remains energized, negative pulses produced in response to vehicles sensed by detector 1l are coupled to counter 25 through front contact 17, while positive pulses produced in response to vehicles sensed by detector 12 are coupled to counter 24 through front contact 18. Thus, vehicles entering the demarcated portion of the traflic lane shown in FIG. 2 are added to the count in counter 25, which has been reset to zero at the end of the iirst interval. Similarly, vehicles sensed by detector 12 are subtracted from counter 24, thereby decreasing the count in counter 24 which at its maximum represented the total number of vehicles entering the demarcated portion of the traHic lane in the irst interval.

At the end of the second interval, relay R1 deenergizes, closing back contact 19. Capacitor 33 now acquires a charge through relay R2. This causes momentary energization of relay R2, in turn momentarily closing front Contact 28 of the relay. The count stored in counter 24 is thereby coupled to integrator 32, and may be read on indicator 44. If the number of vehicles added by detector 11 equals the number ofl vehicles subtracted by detector 12, indicator 44 reads zero. If the number of vehicles added by detector 11 exceeds the number of vehicles subtracted by detector 12, indicator 44 shows a negative number, indicating that more vehicles have entered the demarcated portion of the traic lane during the first interval than have left that portion during the second interval. On the other hand, if the number of pulses subtracted from counter 24 by detector 12 exceeds the number of pulses added to counter 24 by detector 11, indicator 44' shows a positive number, indicating that more vehicles have left the demarcated portion of the traic lane during the second interval than entered the demarcated portion ofthe lane during the irst interval.

Upon deenergization of relay R2, analog memory 32 is returned to its HOLD mode, and indicator 44 retains the reading produced by counter 24 at the end of the second interval. Simultaneously, capacitor 34 discharges through back contact 29 of relay R2, resetting the counter.

During this third interval, which is identical circuitwise to the rst interval, negative pulses are again added to counter 24 through back contact 17 of relay R1 in response to vehicles detected by detector 11. Similarly, positive pulses are applied to counter 25 through back contact 18 of relay R1 in response to vehicles sensed by detector 12. These positive pulses subtract from the maximum count occurring in counter 25 at the end of the second interval and representing the number of vehicles counted by detector 11 during the second interval.

At the end of the third interval, the count stored in counter 25 is applied to analog memory 32 and the counter is thereupon reset to zero. Thus, at the end of the third interval, which corresponds circuitwise to the rst interval, the total count applied to analog memory 32 comes from counter 25. At the end of the second interval, the total count applied to analog memory 32 comes from counter 24. Hence, the rst and second intervals may actually be considered odd and even intervals respectively, since the intervals may be continued indefinitely.

It should be noted that the system time intervals are not necessarily of identical durations. Each counting time interval is related to detected vehicle speed in such man- 9 ner that the interval continues for a period of time which is exactly the proper amount of time for a vehicle to have traversed the demarcated portion of the traffic lane, travelling at a constant speed equal to average vehicular speed as measured during the interval.

At the end of alternate time intervals, alternate counters are coupled to analog memory 32, applying their counts thereto. After each counter has been coupled to the analog memory, the counter is cleared and reset to zero. Negative -pulses are then applied to the cleared counter. On Ithe other hand, positive pulses are applied to the other counter, decreasing the count therein. At the end of the next succeeding interval, the counter last receiving positive pulses provides an output to analog memory 32, and is subsequently cleared. Moreover, the counter which has been receiving negative pulses, now begins receiving positive pulses. Thus, when one counter has vehicles added to it the other counter has vehicles subtracted from it, and vice-versa. The two counters thereby alternate in operation, with one having vehicles added to it as they are sensed by vehicle detector 11, and the other having vehicles subtracted from it as they are sensed by detector 12, during each time interval. All vehicles passing beneath each of the two detectors are thereby accounted for both as they enter and leave the demarcated portion of the trafiic lane.

It is well to observe that each time interval may be made of duration inversely proportional to average vehicle speed, but of a constant fraction of the time required for a vehicle travelling at the average speed to traverse the demarcated portion of the trafiic lane. In such system, the start of the second interval would then be delayed by the remaining time for a vehicle travelling at the average speed to reach the vicinity of detector 12. Thus it is obvious that the greater the fraction, the greater the accuracy and reliability of the system. In the preferred embodiment, the time intervals each continue -for the entire time required to traverse the demarcated portion of the traic lane, since each vehicle is counted thereby, either upon entry or exit, lproviding indications of greater accuracy and reliability. Hence, the aforementioned fraction, as used in the system of FIG. l, is actually one. By counting each vehicle entering and leaving the demarcated portion of one or the other counter, maximum accuracy and reliability are provided, since readings are produced through consideration of every vehicle both upon entry to and egress from the demarcated portion.

As previously mentioned, the reading on indicator 44 is produced by a voltage representing vehicle counts. These counts are actually the difference in counts between those produced -by detector 11 during a first interval and those produced by detector 12 during a second subsequent interval. The voltage analog of these vehicle counts is coupled through phase inverter 36 and diode 37 in the event it represents negative counts, or through diode 38 directly in the event it represents positive counts, to provide a positive input voltage to analog computer circuit 39. A second voltage is provided to analog comparator circuit 39 lfrom count control 40` through back contact 41 of relay R4. This voltage is of negative polarity, and is compared with the voltage of positive polarity applied to the first input of analog comparator 39.

In the event there is a large discrepancy between the counts provided by detector 11 during the first interval and the counts provided -by detector 12 during the second interval, a discontinuity in trafiic flow through the demarcated portion of the traffic lane is in progress. This condition is detected by analog memory 32, which produces a large amplitude output voltage in response thereto. This voltage is then coupled to the first input of comparator 39 through phase inverter 36 and diode 37 in the event it is a negative voltage, or through diode 38 in the event it is a positive voltage, and compared with the present voltage` supplied by count control 41. When the magnitude or absolute amplitude of positive voltage applied to the first input of analog comparator 39 exceeds the magnitude, or absolute amplitude of negative voltage applied to the second input of analog comparator 39, the output voltage of comparator 39 abruptly changes from a large positive value to a large negative value. This voltage is coupled through amplifier 32 which inverts the voltage polarity, energizing relay R4, thereby clearing front contact 42 and providing a signal to utilization means 57. Simultaneously, back contact 41 opens and -front contact 41 closes, applying a new and preferably lower negative voltage to the second input of analog comparator circuit 39. Thus, in order for relay R4 to again deenergize, output voltage produced from analog memory 32 must be of a different and preferably lower value in magnitude, or absolute amplitude, in order to abruptly change the polarity of output voltage from analog comparator 39 back to a positive value, than the magnitude, or absolute amplitude, originally required to change the polarity of output voltage from comparator 39 to negative. When this condition occurs, relay R4 deenergizes, deenergizing the utilization means. This indicates that the discrepancy in counts between those produced by detector 11 during a first interval, and those produced by detector 12 during a second interval, has substantially decreased. This, in turn, is indicative of a return to free-iiowing trafiic conditions within the demarcated portion of the traffic lane of FIG. 2.

I t should be noted that the system is insensitive to gradual changes in traic ow, and is responsive only to marked trafiic changes such as disruptions and discontinuities. This is because the duration of each time interval is inversely proportional to average vehicular speed. Such measurements are extremely useful, since gradual changes in traffic flow occur continuously, and hence should be overlooked, while sudden changes in traffic flow should be detected for facilitating rapid correction thereof. Thus, if speed gradually decreases in an interval, the duration of the interval is lengthened acordingly, so that there is more time in the interval to count the vehicles entering and leaving the demarcated portion of the trafiic lane. Hence the count applied to analog memory 32 does not change to any great extent, and utilization means 57 remains deenergized.

In the event it is desired to make the system responsive to gradual changes in traflic flow for any reason, the time intervals need merely be made of fixed duration less than the time required for a vehicle travelling at the maximum expected speed to traverse the demarcated portion of the traffic lane. Then counts may be made in each time interval, with the intervals separated by the time required for a vehicle to traverse the demarcated portion of the lane travelling at the average measured speed minus the aforementioned fixed duration. Thus, if speed gradually decreases during an interval, less vehicles are counted in the interval, and vice-versa.

A second traffic check in the computer is performed by volume differential circuit 9. In this circuit, trai-lic volume as sensed at detector 11 is continuously compared with traffic volume sensed at detector 12, independent of time intervals demarcated by energization and deenergization of relay R1. This volume difference is continuously averagedv by averaging circuit 47. The average volume difference produced by averaging circuit 47 is presented on meter 48, and may be read in terms of positive or negative vehicles per unit time. A positive reading on meter 48 may arbitrarily indicate a greater trafiic volume at detector 11 than detector 12, while a negative reading on meter 48 would then arbitrarily indicate a greater trafiic volume at detector 12 than at detector 11.

In the event output voltage from averaging circuit 47 is of positive polarity, the voltage is `applied to the first input of analog comparator circuit 52 through diode 50. ACn the other hand, if the output voltage from averaging circuit 47 is of negative polarity, it is inverted through phase inverter 49 and applied to the first input of analog 1 1 comparator 52 through diode 51. The voltage at the first input to analog comparator 52 is then compared with a second voltage applied to the second input of analog comparator 52 from traffic volume control 53 through back contact 54 of relay R5. If the magnitude, or ,absolute amplitude, of positive voltage applied to the first input rof analog comparator S2 increases beyond the magnitude, or absolute amplitude, of negative voltage applied to the second input of analog comparator 52, output voltage of 'analog comparator 52 abruptly changes in polarity from a large positive value to -a large negative value. This negative voltage at the output of comparator 52 is coupled through arnplifier 56, which inverts the polarity of the applied voltage, energizing relay R5. Front contact 54 is thereby closed, applying a new and preferably lower negative voltage to the second input of analog comparator 52. Under these conditions, relay R5 remains energized as long as the volume difference voltage remains above a level determined by the negative voltage now applied to the second input of :analog comparator 52 through front contact 54 of relay R5. During this interval, front contact 55 of relay R5 is closed, energizing utilization means 57 for the purpose `of providing a traffic flow warning signal.

When the volume difference voltage falls below the value provided by front contact 54 to the second input of analog comparator 52, the algebraic sum of voltages applied to the input of lanalog comparator 52 again becomes negative. This causes an abrupt change in output voltage of comparator 52 from a highly negative value Ito a highly positive value. This positive voltage is amplified and inverted through amplifier 56, providing a negative voltage to relay R5. The relay thereby deenergizes, opening front contact 55 and deenergizing utilization means 57. It should be noted that under normal system operation, relays R4 and R5 will be energized and deenergized at approximately identical times. This is because discontinuities in traffic flow are detected by volume differential circuit 9 and count differential circuit 8. However, under certain traffic conditions, relay R4 may be energized while lrelay R5 is deenergized, and viceversa. rIhus, the computer energizes utilization means 57 whenever 4any traffic discontinuity occurs within the demarcated portion of the traffic lane, regardless of the particular form of discontinuity.

Turning now to FIG. 3,'there is shown a schematic diagram of one form of aver-age speed computer 13, shown in block form in FIG. 1. A first relay R11 receives energy from detect-or 11, while a second relay R12 receives energy from detector 12. A capacitor 100 is coupled to the heel of a contact 102 of relay R11. Similar-ly, a capacitor 10'1 is coupled to the heel of a 4contact 104 of relay R12.

A summ-ing resistor 106 is coupled between front cont-act 102 and the input to an operational amplifier 110. Similarly, a summing resistor 108 is coupled between front contact 104 and the input to operational amplifier 110. Back contacts 102 and 104 a-re each coupledy to the source of positive voltage. Thus, when back contact 102 is closed, capacitor 100 acquires a charge. Similarly, when back contact 104 is closed, capacitor 101 acquires a charge.

A front contact 103 of relay R11 and a feedback resistor 107 are coupled in series between input and output of operational amplifier 110. Similarly, a front contact 105 of relay R12 is coupled in series with a feedback resistor 109 between the input and output of operational amplifier 110. A feedback capacitor 111 is also coupled between the input land output of amplifier 110'. Hence, energization of either relay R11 or R12 causes `a momentary impulse to be applied to the input of amplifier 110 through either resistor 106 or 108, respectively. Similarly, energization of relay R11 causes shunting of capacitor 111 with resistor 107, while energization of relay R12 causes shunting of capac-itor 111 with resistor 109.

In operation, computer 13 divides traffic volume by traffic density to provide an output voltage proportional to average speed. Volume information is applied to the input of amplifier 110, while density inform-ation is applied to the feedback circuit around yamplifier 110. More specifically, each time a vehicle is detected by detector 11, capacitor discharges a fixed amount of charge to amplifier 110. Similarly, each time -a vehicle is detected by detector 12, capacitor 101 discharges a fixed amount of charge to amplifier 110. Moreover, relay R11 remains energized for the entire interval in which a vehicle is sensed by `detector 11, whiie relay R12 remains energized throughout an entire interv-al in which a vehicle is sensed by detector 12. Thus, while a vehicle is sensed by detector 11, resistor 107 is shunted across capacitor 111; simil-arly, during the entire interval in which a vehicle is sensed by detector 12, resistor 109 is shunted across capacitor 111. Hence, when a charge is coupled to amplifier from either capacitor 100 or 101, resistor 107 or 109 respectively provides a leakage path for the charge which is transferred to capacitor 111. The sizes of resistors 107 or 109 are so -adjusted that output voltage from amplifier 110 is proportional to traffic volume; that is, proportional to vehicles sensed per unit time. Addition of feedback resistor 107 or 109 across amplifier 110 thereby prevents the yamplifier from operating as a pure integrator, but -rather provides the amplifier with `a leakage path for capacitor 111 Ihaving a predetermined time constant. In this manner, volume information is provided to computer 13. Moreover, since both detectors 11 and 12 are used for sensing vehicles, total volume information from two different locations along the traffic lane is provided to the computer. However, energization of either relay pro vides a separate, independent feedback circuit 'around amplifier 110. The feedback resistors are so selected that volume information applied to the computer is divided by two. This has the effect of providing average traffic volume information to the computer, as sensed by detect-ors 11 and 12.

Traffic `density information is applied to computer 1-3 in the form of feedback paths comprising resistors 107, or 109 for the length of time during which either relay R11 or R12, respectively, remains energized. Each relay remains energized for the entire length of time during which a vehicle is sensed by the detector coupled thereto. Detectors such as those disclosed in Kendall and Auer application Ser. No. 808,736, filed Apr. 24, 1959, now -U.S. Patent 3,042,303, are highly suitable for supplying density information to thecomputer.

Although computer 13 provides speed information by dividing traffic volume by traffic density, the computer actually operates on lane occupancy information, rather than density information. The parameter of lane occupancy is fully described in Kendall and Auer application Ser. No. 78,410, filed Dec. 27, 1960, now U.S. Patent No. 3,233,084, issued Feb. l, 1966, wherein'it is defined as being the portion of a highway which is vehicle-occupied, and may be expressed as a percentage. Thus, when no vehicles are passing along the traffic lane, for example, lane occupancy is zero. However, lane occupancy approaches 100% when vehicles are almost bumper-to bumper along the trafiic lane. The system herein disclosed measures lane occupancy separately at detectors 11 and 12, and averages the two measurements in computer 13.

It should be noted that lane occupancy is not necessarily rel-ated to traffic volume. For example, when vehicles are travelling with substantial spacing between them but at a relatively high speed, lane occupancy may -be low but traffic volume may nevertheless be quite high. On the other hand, when vehicles are bumper-to-bumper but are not moving, whatever the reason, lane occupancy is substantially 100%, but traffic volume under -those conditions is zero.

Lane occupancy however, it related to traic density. Density is expressed in terms of vehicles per unit length of highway. Lane occupancy on the other hand is ex- 13 pressed in terms of percentage of a highway, or segment thereof, occupied by vehicles. Therefore, lane occupancy may -be expres-sed in terms of density multiplied by a factor equal to the average length of vehicles travelling along the traffic lane.

Therefore, average speed is computed by computer 13 which divides average trafiic volume by average traffic density to arrive at average trafic flow velocity within the demarcated portion of the trafiic lane. Expressed mathematically, for a speed computation made at detector 11 only:

let

While relayl R11 is deenergized, capacitor 100 charges a-ccording to the equation Q,=CE Each time relay R11 is energized, the charge on capacitor 100 is tran-sferred to capacitor 111 through resistor 106.

Therefore, over a period of several minutes, charge is supplied to capacitor 111 at the rate Q minute While relay R11 is energized, capacitor 111 is also discharged through resistor 107 by an amount of charge equal to VCE Where I is the average current through resistor 107, expressed in amperes, and t is the length of time, in seconds, yduring which relay R11 is energized, which equals the length of time during which a vehicle is sensed by detector 11. Thus, over a period of several minutes, discharge from capacitor 111 occurs at the rate Q E minute-60HL Under equilibrium conditions, that is, when the charge on capacitor 111 is correctly representing the average speed then existing, the charging and'discharging rates are equal. Thus,

Solving for E0,

VCER E- eoL Multiplying the numerator and denominator by V CER 5280 However, density is related to occupancy by the equation Hence,

V OER 5280 EO-" Volume, letting S=average speed,

Since average speed=deTsity OER Where speed is measured in miles per minute, or

CER Eri-SSS 60A Where speed is measured in miles per hour.

Hence, E0 is proportional to average speed at detector 11, where an average vehicle length is assumed.

From the foregoing therefore, it is obvious that a speed calculation may be made by computer 13 from inform-ation supplied by detector 11. In similar fashion, speed may be calculated from information supplied by detector 12. Since each detector provides a charge to amplifier 110 from a separate capacitor and provides a separate feedback resistor across the amplifier, both detectors can function simultaneously, so that otuput voltage produced from the computer is proportional to the average of speeds measured at detectors 11 and 12.

FIG. 4 is a schematic diagram of volume difference computer 4,6, shown in block form in FIG. 1. This computer comprises an operational amplifier 120 having a pair of inputs coupled from negative pulse generator 26 and positive pulse generator 27 of FIG. 1. Negative pulses are coupled to the input of amplifier 120 through a summing resistor 121, While positive pulses are coupled to the input of amplifier 120 through a summing resistor 122,. A feedback capacitor 123 is coupled between the input and output of amplifier 120, while a feedback resistor 124 is similarly coupled between input and output of amplifier 120.

Operation of this computer is similar to that described for volume calculations made by computer 13. Thus, positive pulses applied to the amplifier tend to charge capacitor 123 to a polarity whereby the plate coupled to the input side of amplifier 120 `becomes positive with respect to the lother plate, while negative pulses coupled to the amplifier tend to charge capacitor 1,23 to the opposite polarity.

It should be noted that constant energy pulses are provided by pulse generators 26 and 27. Thus for each actuation of either detector, a pulse of constant energy be it positive or negative, is applied to amplifier 120. Capacitor 123 tends to store these pulses. Hence, in the event more negative pulses than positive pulses are coupled to amplifier 120, capacitor 123 acquires a charge whereby the plate coupled to the input side of amplifier 120 becomes negative. Similarly, in the event an excess of pulses are applied from positive pulse generator 27, capacitor 123 swings in the direction of opposite polarity. The voltage stored on capacitor 123 is provided at the output of amplifier 120, in a manner well known in the art.

Resistor 124 provides a leakage path for capacitor 123, preventing computer 46 from operating as an integrator circuit. Thus, if no input pulses are provided to the computer, output voltage gradually decreases in accordance with the RC time constant of capacitor 123 and resistor 124. Hence, pulses must be produced from generators 26 and 27 in order to maintain an output voltage from the computer.

Since negative voltage pulses are produced in response to vehicle detections at detector 11, while positive voltage pulses are produced in response to vehicle detections at detector 12, the voltage pulses produced in response to the aforementioned vehicle detections are algebraically added through summing resistors 121 and 122 prior to yapplication to amplifier 120. Thus, output voltage from volume difference computer 46 is proportional to the difference in traffic volume between that measured at detector 11 and that measured at detector 12.A

Output voltage from computer 46 is an electrical analog of traf'lic volume as may be seen from the following mathematical derivation. For simplicity, assume that negative and positive pulse generators 26 and 27 each comprises a relay driven contact which charges a capacitor when the relay is deenergized and discharges the capacitor to computer 46 when the relay is energized. Assume further that the relay is operated in response to vehicle detections. Hence, positive pulse generator 27 is analogous to capacitor 100 and contact 102 in average speed corn puter 13. Negative pulse generator 26 is also analogous to capacitor 100 and contact 102 of computer 13, with the exception that the relay back contact is coupled to the negative voltage source.

FIG. is a schematic diagram of one form of negative pulse generator 26 which may be used in the system of FIG. 1. A relay R13 is operated in response to vehicle detections by detector 11. Each time the relay is energized, a capacitor 130 discharges a negative charge to volume difference computer 46; upon deenergization of the relay, the capacitor again acquires a negative charge.

FIG.' 6 schematically illustrates positive pulse generator 27 of FIG. l. In this generator, a relay R14 is coupled to detector 12, and is responsive to vehicle detections produced therefrom. Upon energization of the relay, a capacitor 135 discharges a positive pulse to the volume difference computer; upon deenergization of the relay, the capacitor is again charged from the positive Voltage source.

Returning to FIG. 4, and letting then while relay R13 is deenergized, capacitor 130 charges according to the equation QN: CEN

Each time relay R13 is energized, this charge is transferred to capacitor 123 through resistor 121. Therefore, over a period of several minutes, charge is supplied to capacitor 123 as a result of operation of detector 11 at the rate minute :V11 CEN Similarly, the charge rate of capacitor 123 as a result of operation of detector 12 is minute Continuous discharge of capacitor 123 occurs through resistor 124 at the rate Q sono minute- Rf When equilibrium is attained, that is, when the charge on capacitor 123 is correctly representing the average volume dijerence, the charge and discharge rates must add up to zero. Hence l 5 Solving for En,

and E0 therefore is directly proportional to the difference in trafiic volumes measured at detectors 11 and 12, since C, EP and Rf are all constants.

It should be noted that in the event only a single detector is operated, computer 46 acts solely as a volume computer. For example, if only detector 12 were utilized, then the computer would operate according to the following expression:

E GG=VHCEP Hence,

CE R E0=V12 61) t vides a first feedback path around amplifier 140, with v the anode of diode 143 coupled to the input of amplifier 140. A second feedback circuit around amplifier is provided by a seriesconnected diode and resistor 146, with the cathode of diode 145 coupled to the input of amplifier 140. The cathode of diode 143 is resistively coupled to the source of positive voltage, while the anode of diode 145 is resistively coupled to the source of negative voltage.

In operation, assume the algebraic sum of voltages applied to the input of amplifier 140 is of negative polarity. The phase inversion inherent in operational amplifiers causes a positive output voltage to be provided from amplifier 140. Hence, diode 145 conducts, since it is biased in the forward direction.

As the polarity of input voltage swings in a positive direction, diode 145 begins to cut off. This opens the feed- |back loop provided through resistor 146, so that the high gain of amplifier 140 then cuts off diode 145 sharply by increasing its anode voltage in a negative direction. Diode 143 then limits the amplifier output voltage to a predetermined negative value.

When the `algebraic sum of the input voltage polarity again swings negative, diode 143 begins to cut off. This opens the feedback circuit through resistor 144, so that the high ampliiier gain cuts diode 143 off sharply by increasing its cathode voltage in a positive direction. Diode 145 then limits the amplifier output voltage to a preselected positive value. The net result is that when the polarity ofthe algebraic sum of input voltages applied to amplifier 140 reverses, output voltage abruptly changes from a constant value of one polarity to a constant Value of the opposite polarity, and remains at the new constant value and polarity until the polarity of input voltage again changes, Vat which time the output volage returns to the former constant Voltage and polarity.

FIG. 8 is a schematic diagram of a typical counter as used in the block diagram of FIG. l. The counter com prises `an amplifier having a feedback capacitor 151 and an input resistor 152 coupled thereto. This portion of the counter is a common integrator circuit.

Resetting of the counter is accomplished through a relay R13, which receives reset pulses at the end of each full counting cycle. Each counting cycle encompasses two time intervals as demarcated by relay R1 of FIG. 1. The reset pulse momentarily energizes relay R13, which opens a back contact 153, thereby removing input voltage from the counter. Moreover, front contact 153 closes, providing a discharge circuit for capacitor 151 through resistor 152. During the interval in Which relay R13 is energized, capacitor 151 discharges substantially completely. The counter is thus reset to zero. Subsequent deenergization of relay R13 again completes the input circuit for the counter, permitting the next counting cycle tobegin.

Turning next to FIG. 9, there is shown a schematic diagram of averaging circuit 47, shown in block form in FIG. 1. This circuit comprises an operational amplifier 160 having a feedback capacitor 161 shunted across the input and output. A summing resistor 163 is coupled to the input of the operational amplifier. A feedback resistor 162 is shunted across the amplifier output and resistor 163. The junction between resistors 162 and 163 is coupled to ground through a resistor 164. Input signals are applied to the junction between resistors 162 and 163 through an input resistor 165.

Averaging circuit 47 is therefore basically an integrating circuit having a resistor shunted across the amplifier and summing resistor, thus providing a leakage path for the capacitor through resistors 162 and 163. The circuit introduces a long time constant, which s necessary in order to provide an output signal of amplitude representing the average of input signal amplitude taken over a period of time. Resistor 164 effectively produces .a scale factor for the averaging circuit by scaling down the voltage amplitude applied to the input of amplifier 160, since it functions in combination with resistors 162 and 165 as a voltage divider circuit.

When input voltage to averaging circuit 47 swings in a direction of one polarity, output voltage from the circuit tends to swing in a direction of opposite polarity. This voltage of opposite polarity is then fed back through resistors 162 and 163 to the input side of amplifier 160, in a ydirection tending to oppose the input voltage applied to the averaging circuit, Over a long period of time however, the circuit tends to stabilize, provided the input voltage stabilizes. A varying input voltage however, prevents the circuit from stabilizing, due to the long time constant inherent therein.

It should be noted that the averaging circuit views the input quantity through an RC network comprising series resistor 163 and shunt capacitor 161. 'Ihe RC network provides an exponential delay csar-acteristic. Statistically, the result of viewing a changing quantity through an eX- ponential delay is to obtain a modified running average.

If an RC network with a 100 second time constant is used, the modified running average is based on a 100 second interval, and as inputvinformation for each second is added to the running sample, 1% of the running sample is discarded. The modified running average differs from what may be termed a normal running average in that for each 1% of the averaging time, 1% of the running sample is discarded, instead of the precise bit of information vadded during the previous sampling interval. FIG. 9 is thus a practical circuit which yields very long eX- ponential time constants. As is usual in analog circuits, the function of amplifier 160 is to continually and automatically adjust its output voltage so as to maintain its input voltage practically at zero.

Operation of the averaging circuit may be illustrated mathematically as follows:

Let E1 represent averaging circuit input voltage, Let E2 represent averaging circuit output voltage, Let E3 represent voltage at a point common to resistors 162, 163, 164 and 16s,

Let Eg represent input voltage to amplifier 160, Let C represent the capacitance of capacitor 161,

lLet R represent the ohmic value of resistor 165,

Let R20 represent the ohmic value of resistor 162, Let R30 represent the ohmic value of resistor 164,

18 Let R40 represent the ohmic value of resistor 163, and Let q represent the instantaneous charge on capacitor 161. The voltage lacross capacitor 151 may be expressed as Furthermore, all current fiowing through resistor 163 serves to charge capacitor 161,l so that 2 ggg-E.

d# R40 Assuming operational amplifier maintains its input voltage at zero, Equation 1 becomes and Equation 2 becomes 4) im@ di R40 Summing all currents entering the junction common t0 resistors 162, 163, 164 and 165 Iyields Eg-El l F13-E2 I E3-0 E3-0=0 R10 T R20 T R30 R40 which may be rewritten as R20 R20 R20 R20) 1 RwElfEz E3 LRIUJFRSOLM Letting then Equation 5 may be rewritten as Assuming q=0 when t=0, the solution to this differential equation is 9) t Q=ECE1 1 8 kRaoO Rio Substituting Equation 9 into Equation 1, 10 t e-kruuo) Equation 10 is of the same form as the classical equation for charging a capacitor through a series resistor with the following two exceptions:

First-A voltage gain may be obtained by setting resistor 162 greater than resistor 165 if desired, and

Second- The time constant contains a multiplying factor k and hence is equal to the product ofR40C and k.

In actual operation, resistor 162 is normally left equal to resistor 165 since the circuit is intended primarily for providing a long delay, rather than a change in scale. To obtain a long delay, k is made very large. In this manner, very long effective time constants are obtained without the necessity of using unreasonably large values of lresistance and capacitance. For example, a ten minute time constant may easily be obtained using values of 6 megohms for resistor 163, 10 microfarads for capacitor 161 and 10 for k. Referring to the expression for k it is seen that if R and R20 are each 6 megohms as well as R40, a value of 10 may be obtained for k by letting R30 equal 0.857 megohm. By further reducing the value of R30, much larger time constants may be obtained.

FIG. 10 is a schematic diagram of analog memory circuit 32, shown in block form in FIG. 1. This circuit comprises an operational amplifier 170 having a feedback capacitor 171. Output from counter 24 is coupled through a pair of series-connected resistors 172 and 173 to the output of amplifier 170. Similarly, output from counter 25 is coupled through a pair of series-connected resistors 174 and 17S to the output of amplifier 170, Input to amplifier 170 is coupled from the output of counter 24 through resistor 172 in series with front contact 28 of relay R2, or from counter 25 through resistor 174 in series with front contact 30 of relay R3.

In operation, while counters 24 and 25 are counting, relays R2 and R3 are deenergized. The amplifier is then operated in its HOLD mode. Any charge stored on capacitor 171 provides an input to the amplifier which thereby provides a constant output voltage accordingly. At the end of -a full cycle of counts by counter 24, relay R2 is momentarily energized, as explained supra, thereby coupling output voltage from counter 24 to amplifier 170 and coupling resistor 173 in a feedback path around the amplifier, in parallel with capacitor 171. Under these conditions, amplifier 170 output voltage becomes equal to counter 24 output voltage multiplied by a factor equal to the ohmic value of resistor 173 divided by the ohmic value of resistor 172. Obviously, a phase inversion also takes place, so that the polarity of output voltage from amplifier 170 is opposite to the polarity of output voltage from counter 24.

When relay R2 deenergizes, counter 24 is reset to zero, as previously described. Simultaneously, the input circuit to amplifier 170 is opened. The amplifier then retains the reading last applied to it from counter 24, since the counter voltage applied thereto is stored on capacitor 171.

Similarly, when relay R3 energizes, output from counter 25 is coupled to the input of amplifier 170 through front con-tact 30. This changes the voltage stored on capacitor 171 to a voltage corresponding to that provided by counter 25 multiplied by a factor equal to the ohmic value of resistor 175 divided by the ohmic value of resistor 174. When relay R3 next deenergizes, capacitor 171 remains charged to the amplitude of voltage applied thereto from counter 25, and a new output voltage is thereby provided from the analog memory circuit, Simultaneously, counter 25 is reset through back contact 31 of relay R3.

Thus, there has been shown means for maintaining traffic surveillance within a defined zone, for the purpose of detecting disruptions and discontinuities in trafiic iiow within the zone. Disruptions and discontinuities may be approximately located bydetermining the polarity of output voltage from analog memory 32. For example, excessive negative pulses applied to counters 24 and 25, showing up as a net negative voltage Iat the output of analog memory circuit 32, represent a greater number of detections by detector 11 than by detector 12. This indicates that vehicles are entering the defined zone, although flow out of the zone is obstructed. Hence the obstruction is located somewhere along the trafiic lane beyond detector 11. Similarly, in the event counters 24 and 25 receive an excessive number of positive pulses, providing a positive output volt-age from analog memory circuit 32, detector 12 is sensing more vehicles than detector 11. This indicates that an obstruction to traflic flow is located somewhere along the traffic lane prior to the location of detector 12. Similar information can be provided by observation of `the amplitude and polarity of output voltage from averaging circuit 47 as read on meter 48.

FIG. l1 is' a simplified block diagram of a second ernbodiment of count differential circuit 8 of FIG. l. By using a variable delay unit, a continuous comparison of trafiic'volumes at inbound detector 11 and outbound detector 12 may be accomplished. Use of counters 24 and 25 and relay R1 of FIG. 1 is thereby obviated.

Outputs from detectors 11 and 12 are applied to average speed computer 13. Output of computer 13 thereby provides a control signal of amplitude proportional to average speed as measured at detectors 11 and`12. This control signal is applied to .a variable delay unit 180, which comprises temporary storage means wherein the duration of storage is inversely proportional to the output voltage amplitude of average speed computer 13. The delay unit delays negative pulses produced by negative pulse generator 26 in response to vehicle detections by detector 11.

After each negative pulse from pulse generator 26 is delayed by the variable delay unit, it is applied to a first input of a volume difference computer 181. This computer is identical in configuration and operation to that shown in detail in FIG. 4. A second input to the volume difference computer is provided from positive.

pulse generator 27 in response to vehicle detections by detector 12. Output from volume difference computer 181 is coupled through circuitry identical to that shown coupled to the output of analog memory 32 in FIG. 1.

In operation, negative pulses from pulse generator 26, corresponding to inbound vehicle detections, are delayed in variable delay unit for a length of time inversely proportional to output voltage and amplitude from average speed computer 13. Positive pulses from pulse generator 27, corresponding to outbound vehicle detections, and the delayed negative pulses from pulse generator 26 are applied simultaneously to volume difference computer 181. Thus, if trafiic volume at detector 12 is identical to traffic volume at detector 11 after a delay corresponding to the length of time required for a vehicle travelling at the computed average speed to progress from detector 11 to detector 12, output from volume difference computer 181 is zero. In the event traffic volume at detector 12 exceeds the delayed trafiic volume at detector 11, a negative output is produced by volume difference computer 181. If this negative output rises above a predetermined amplitude, utilization means 57 is energized and the polarity of indication on meter 44 indicates that a trafic obstruction is located along the trafiic lane somewhere ahead of outbound detector 12. On the other hand, if the delayed traic volume at kdetector 11 exceeds trafiic volume at detector 12, a positive output is provided by volume difference computer 181, which energizes utilization means 57 in the event this positive output amplitude exceeds a predetermined value. The positive indication on meter 44 indicates that a trafn'c obstruction is located along the trafiic lane somewhere behind inbound detector 11.

FIG. l2 is an illustration of one type of variable delay unit 180 which may be used in the system of FIG. 11. A DC motor is `driven from average speed computer 13 through a bridge rectifier 191. The bridge rectifier assures that only a single voltage polarity is applied to the motor. Hence, the motor is driven in a single direction at a speed directly proportional to amplitude of output voltage from average speed computer 13. The motor in turn drives a tape transport mechanism 192 carrying an endless belt of magnetic tape 193. A record head 194 and a playback head 195 are spaced along the tape a fixed distance apart from each other. An erase head 197 is situated along the tape at a location prior to the location of the record head. This head provides continuous eradication of signals on the tape prior to recording thereon. Record head 194 receives input voltage from negative pulse generator 26, while output voltage from playback head 195 is applied to volume difference computer 181 through an amplifier 196. l

In operation, DC motor 190 is driven in a clockwise direction at a speed directly proportional to amplitude of output voltage from average speed computer 13. Each negative pulse produced by pulse generator 26 is recorded on tape 193 at record head 194. When a pulse so recorded reaches playback head 195, an output pulse is coupled through amplifier 196 to the first input of volume difference computer 181. If the vehicle which initiated the recorded negative pulse when it passed detector 11 reaches detector 12 at the time when the portion of tape 193 carrying the negative pulse passes playback head 195, simultaneous positive and negative pulses are applied to volume difference computer 181 of FIG. 11, and meter 44 of FIG. 11 reads zero. In the event a recorded negative pulse initiated by a vehicle passing detector 11 reaches playback head 195 before the vehicle actually reaches detector 12, meter 44 of FIG. 11 reads positive, since a net negative voltage is applied to the input of volume difference computer 181. On the other hand, if the vehicle which initiates a negative pulse on tape 193 by passing detector 11 arrives at detector 12 before the recorded negative pulse on tape 193 reaches playback head 195, meter 44 of FIG. 11 reads negative, since the input to volume difference computer 181 is positive. In this fashion, pulses arriving at volume difference computer 181 from either variable delay unit 180 only or positive pulse generator 27, only cause a large negative or positive voltage respectively to be built up at the input to volume difference computer 181. Hence, the output voltage from computer 181 builds to a large positive or negative Value, respectively, energizing utilization means 57 in a manner previously described. f

The system therefore provides two checks on traffic disruption and discontinuities within the demarcated portion of the traffic lane. The first check is provided by alter nately counting the number of vehicles entering the demarcated portion of the traic lane during a first interval and counting the number of vehicles leaving the demarcated portion of the traffic lane during a second subsequent interval. The difference between counts and polarity of the difference provide an indication of conditions within the demarcated portion of the trafiic lane.

The second check is provided by constantly measuring the volume at both entry and egress detectors, and maintaining a constant running check on the measured volurnes. The amplitude and polarity of difference between the measured volumes then provide information as to conditions within the demarcated portion of the trafiic lane.

Although but several embodiments of the present invention have been described, it is to be specifically understood that these forms are selected to facilitate in disclosure of the invention rather than to limit the number of forms which it may assume; various modifications and adaptations may be applied to the specific forms shown to meet requirements of practice, without in any manner departing from the spirit or scope of the invention.

What I claim is:

1. Means for detecting and locating an obstruction to vehicular travel within a traffic lane comprising first and second vehicle detection means spaced in the direction of traffic flow, means responsive to both said detection means for generating successive odd and even time intervals of duration inversely proportional to average speed of trafiic flow, counting means, negative pulse generating means responsive to said first vehicle detection means, positive pulse generating means responsive to said second vehicle detection means, and switching means responsive to said time interval generating means coupling said negative pulse generating means to the counting means during alternate intervals and said positive pulse generating means to the counting means during the remaining intervals.

2. Means for detecting and locating an obstruction to vehicular travel within a traffic lane comprising first and second vehicle detecting means spaced in the direction of traffic flow, means responsive to both said detecting means for generating first and second time intervals of duration inversely proportional to average speed of traffic flow at the outset of each said interval, counting means, negative pulse generating means responsive to said first vehicle detecting means, positive pulse generating means responsive to said second vehicle detection means, and switching means responsive to said time interval generating means coupling said negative pulse generating means to the counting means during one of the intervals and said positive pulse generating means `to the counting means during the remaining interval.

3. In a system for detecting and locating traf'lic disruptions and discontinuities, a pair of vehicle detecting means, each said detecting means `situated at a separate location along a traic lane, means measuring average speed of vehicular traffic, means integrating said average speed with respect to time, counter means adding counts provided by one of said vehicle detecting means and subtracting counts provided by the other of said vehicle detecting means, and relay means coupled to said integrating means and energized when said integrated speed exceeds a predetermined value, said relay means coupling either of said detecting means to said counter means.

4. Means for detecting and locating an obstruction to vehicular travel within a traffic lane comprising first vehicle detection means situated at a first location along the traffic lane, second vehicle detection means situated at a second location along the traffic lane, means responsive to the first detection means for generating a first time interval of duration equal to spacing between the first and second dete-ction means divided by average speed of traffic flow, means responsive to the second detection means for generating a second time interval of duration equal to spacing between the yfirst and second detection means divided by average speed o'f traffic fiow, counting means, first pulse generating means responsive to the first vehicle detection means, second pulse generating means responsive to the second vehicle detection means, and switching means responsive to said first and second time interval generating means coupling the first pulse generating means to the counting means during the first interval and the second pulse generating means to the counting means during the second interval.

5. In a system for detecting and locating trafiic disruptions and discontinuities, a pair of vehicle detecting means, each said detecting means separately located along a traffic lane, means providing a voltage analog of average vehicular trafiic speed, means integrating said average speed voltage with respect to time, a pair of counter means, relay means coupled to said integrating means and energized when said integrated speed voltage exceeds a predetermined value thereby defining a boundary be tween time intervals, said relay means coupling one of the detecting means to one of the counter meansand the other of the detecting means to the other of the counter means during a first time interval whereby said one counter means adds counts while said other counter means subtracts counts and coupling said one counter means to said other detecting means and said other counter means to said one detecting means during the next time interval whereby said other counter means adds counts and said one counter means substracts counts.

6. The system of claim 5 including analog memory means and switching means responsive to said relay means for momentarily coupling said one counter means to said analog memory means upon each energization of said relay means and momentarily coupling said other counter means to said analog memory means upon each deenergizati-on of said relay means.

7. In a system for detecting and locating trafiic disruptions yand discontinuities, a pair of vehicle detecting means, each said detecting means separately located along a traffic lane, means measuring average speed of vehicular traffic, means integrating said average speed with respect to time, counter means adding counts provided by one of said vehicle detecting means and subtracting counts provided by the other of said vehicle detecting means, and two-state switching means coupled to said integrating means and actuated from a first to a second state when said integrated speed exceeds a predetermined value, said switching means coupling either detecting means to said counter means.

8. In a system for detecting and locating traffic disruptions and discontinuities, a pair of vehicle detecting means, first pulse generating means responsive to a first of said vehicle detecting means and second pulse generating meansresponsive to the second of said vehicle detecting means, first and second counter means, means generating odd and even time intervals, and two-state switching means actuated in response to said odd and even time intervals for coupling the first pulse generator to the first counter means and the second pulse generator tothe second counter means during odd intervals and for coupling the first pulse generator to the second counter means and the second pulse generator to the first counter means during even intervals.

9. The system of claim 8 including analog memory means, and additional switching means responsive to said two-state switching means for couplingy either of said counter means to said analog memory means.

10. Means for detecting and locating an obstruction to vehicular travel within a traffic lane comprising first and second vehicle detection means spaced apart from each other along the trafiic lane, means responsive to the first detection means for generating a first time interval of duration equal to spacing between the first and second detection means divided by average speed of traffic flow, means responsive to the second detection means for generating a time interval of duration equal to spacing between the first and second detection means divided by average speed of traffic flow, first and second counting means, negative pulse generating means responsive to the first vehicle detection means, positive pulse generating means responsive to the second vehicle detection means, and switching means responsive to said first and second time interval generating means coupling the negative pulse generating means to the first counting means and the positive pulse generating means to the second counting means during the first interval and the positive pulse generaitng Ameans to the first counting means and the negative pulse generating means to the second counting means during the second interval.

11. The means for detecting and locating an obstruction to vehicular travel within a traffic lane of claim 10 including analog memory means and means responsive to the switching means for momentarily coupling either of said counting means t-o the analog memory means upon each actuation of the switching means.

12. Means for detecting and locating an obstruction to vehicular travel along a traf-lie lane comprising first vehicle detecting means located at a first location along the lane, second vehicle detecting means located at a second location along the lane, negative pulse generating means coupled to the first vehicle detecting means, positive pulse generating means coupled to the second vehicle detecting means, means algebraically totaling negative and positive pulses produced from said negative and positive pulse generating means, and means averaging the output from said algebraic totaling means.

13. In a system for detecting and locating traffic disruptions and discontinuities within a demarcated portion of a traffic lane having first vehicle detecting means situated at one end of the portion and second vehicle detecting means situated at ythe other end of the portion, a volume difference computer comprising operational amplifier means, capacitive feedback means shunted across said amplifier, resistive feedback means shunted across said amplifier, negative pulse generating means coupled to the first vehicle detecting means, positive pulse generating means coupled to the second vehicle detecting means, resistor means coupling the output from the negative pulse generating means to the input of the operational amplifier, and resistor means coupling the output from the positive pulse generating means to the input of the operational amplifier means.

14. In a system for detecting and locating traffic disruptions and discontinuities along a trafiic lane having vehicle detecting means situated along the lane, a traffic speed computer comprising operational amplifier means, feedback capacitor means shunted across said operational amplifier means, resistor means coupled to the input of said operational amplifier means, additional circuit means coupled to the input of said operational amplifier means, second capacitor means, a voltage source, and means responsive to said vehicle detecting means coupling said second capacitor means to the voltage source while no vehicle is detected by said vehicle detecting means and coupling said second capacitor means to said additional circuit means and said resistor means to the output of said operational amplifier means during the interval in which a vehicle is sensed by the vehicle detecting means.

15. The speed computer of claim 14 wherein said addtional circuit means comprises additional resistor means.

16. In a system for detecting and locating trafiic disruptions and discontinuities within a demarcated portion of a trafiic lane having first vehicle detecting means situated at one end of the portion and second vehicle detecting means situated at the other end of the portion, an average speed computer comprising operational amplifier means, feedback capacitor means shunted across said operational amplifier means, first and second resistor means coupled to the input of said operational amplifier means, first and second input circuit means coupled to the input of said operational amplifier means, second and third capacitor means, a voltage source, means responsive to said first vehicle detecting means coupling said second capacitor means to the voltage source during intervals in which no vehicle is sensed by said first detecting means and coupling said second capacitor means to said firstV input circuit means and said first resistor to the output of said operational amplifier means during intervals in which a vehicle is sensed by said first detecting means, and means responsive to said second vehicle detecting means coupling said third capacitor means to the voltage source while no vehicle is detected by said second detecting means and coupling said third capacitor means to said second input circuit means and said second transistor means to the output of said operational amplifier means during intervals in which a vehicle is sensed by said second detecting means.

17.r The average speed computer of claim 16 wherein said first and input circuit means respectively comprise third and fourth resistor means.

18. In a system for detecting and locating traffic disruptions and discontinuities along a traffic lane having vehicle detecting means situated along the lane, a traffic speed computer comprising an analog integrator circuit having a pair of inputs, capacitor means, a voltage source, and means responsive to said vehicle detecting means coupling said'capacitor means to the voltage source during intervals in which no vehicles are sensed by said vehicle detecting means and coupling said capacitor means to one integrator circuit input and the second integrator circuit input to the integrator circuit output during intervals in which a vehicle is sensed by the vehicle detecting means.

19. In a system for detecting and locating an obstruction to vehicular travel along a traffic lane the combination comprising lirst and second 'Vehicle detecting means spaced apart from each other along the lane, negative pulse generating means responsive to the first vehicle detecting means, positive pulse generating means responsive to the second vehicle detecting means, means responsive to both said detecting means for generating first and second time intervals of duration inversely proportional to average speed of traffic flow, counting means, switching means responsive to said time interval generating means coupling said negative pulse generating means to the counting means during one of the intervals and said positive pulse generating means to the counting means during the remaining interval, utilization means, means coupling output from said counting means to said utilization means, means algebraically totaling negative and positive pulses produced from said negative and positive pulse generating means, and means coupling output from said algebraic totaling means to said utilization means.

20. In a system for detecting and locating traffic disr-uptions and discontinuities, a pair of Vehicle detecting means, each said detecting means separately located along a traflic lane, means responsive to said detecting means providing tratc volume information, means responsive to said detecting means provide traic density information, means dividing the volume information by the density information to provide a voltage analog of average trafc speed, means integrating said average speed with respect to time, counter means adding counts provided by one of said vehicle detecting means and subtracting counts provided by the other of said vehicle detecting means, and two-state switching means coupled to said integrating means and actuated from a lirst to a second state when said integrated speed exceeds a predetermined value, said switching means coupling either detecting means to said counter means.

21. A long time constant averaging circuit comprising a single operational amplifier having an input and an output, a capacitor connected between said input and said output, a signal source, circuit means coupling a signal from said source to said input of said amplifier, said circuit means comprising a resistor connected between said source and a circuit junction, a single resistor connected between said junction and said input, means comprising an ohmic connection for coupling a signal from said output of said ampliiier to said junction, and a connection to ground from said junction consisting of a resistive circuit element.

22. Apparatus for detecting and locating an obstruction to vehicular traffic along a predetermined portion of a traic lane comprising, rst vehicle detector means responsive to vehicles entering said portion and second vehicle detector means responsive to vehicles leaving said portion, means for timing successive rst and second time intervals each of a duration dependent upon average velocity of vehicles in said predetermined portion, vehicle speed responsive means for controlling said timing means to time space successive of said time intervals by an amount dependent upon the speed of vehicles in said portion, counting means responsive to said timing means for counting the vehicles detected by said first vehicle detector throughout the first of said intervals and for counting the vehicles detected by said second vehicle detector throughout the second of said intervals, and means responsive to thediference in counts registered by said co-unting means in said first and second time intervals for producing an output manifestation representative of an obstruction to traffic.

23. The apparatus of claim 22 in which said vehicle speed responsive means controls the time spacing of said timed intervals to be inversely proportional to vehicle speed.

24. The apparatus of claim 23 in which said vehicle speed responsive means controls the time spacing of said first and second intervals to be substantially equal to the travel time of vehicles between said first and second vehicle detector means.

25. The system of claim 24 in which each time interval is substantially equal in length to said time spacing determined by said vehicle speed responsive means.

References Cited UNITED STATES PATENTS 2,983,880 5/1961 McFadden 328-127 2,999,999 9/1961 Bartelink 235--150-24 X 3,059,232 10/1962 Barker 23S-150.24 X 3,097,295 7/1963 Williams 23S-150.24 X 3,185,959 5/1965 Barker 23S- 150.24 X 3,231,724 1/1966 Andrews 235--183 X 3,231,728 1/1966 Kusto 235--183 3,237,154 2/1966 Barker 23S-150.24 X 3,249,925 5/1966 Single et al 23S-183 X MALCOLM A. MORRISON, Primary Examiner. I. KESCHNER, I. F. RUGGIERO, Assistant Examiners. 

1. MEANS FOR DETECTING AND LOCATING AN OBSTRUCTION TO VEHICULAR TRAVEL WITHIN A TRAFFIC LANE COMPRISING FIRST AND SECOND VEHICLE DETECTION MEANS SPACED IN THE DIRECTION OF TRAFFIC FLOW, MEANS RESPONSIVE TO BOTH SAID DETECTION MEANS FOR GENERATING SUCCESSIVE ODD AND EVEN TIME INTERVALS OF DURATION INVERSELY PROPORTIONAL TO AVERAGE SPEED OF TRAFFIC FLOW, COUNTING MEANS, NEGATIVE PULSE GENERATING MEANS RESPONSIVE TO SAID FIRST VEHICLE DETECTION MEANS, POSITIVE PULSE GENERATING MEANS RESPONSIVE TO SAID SECOND VEHICLE DETECTION MEANS, AND SWITCHING MEANS RESPONSIVE TO SAID TIME INTERVAL GENERATING MEANS COUPLING SAID NEGATIVE PULSE GENERATING MEANS TO THE COUNTING MEANS DURING ALTERNATE INTERVALS AND SAID POSITIVE PULSE GENERATING MEANS TO THE COUNTING MEANS DURING THE REMAINING INTERVALS. 